Fuel cell system and control method thereof

Abstract

A fuel cell system includes a fuel cell, a fuel gas supply/exhaust portion, an oxidant gas supply/exhaust portion, a cooling portion, and a controller. The controller performs at least one of a transient increase control process and a transient decrease control process. In the transient increase control process, the controller determines whether a temperature of a coolant is in a transient increase state. In the transient increase state, the controller performs an oxidant gas pressure increase process. In the transient decrease control process, the controller determines whether the temperature of the coolant is in a transient decrease state. In the transient decrease state, the controller performs at least one of the oxidant gas pressure increase process and an output increase process. In the output increase process, the controller controls the fuel cell to generate an output higher than a target output corresponding to a request output.

What is claimed is: 
     
       1. A fuel cell system comprising:
 a fuel cell configured to generate a power by an electrochemical reaction between a fuel gas and an oxidant gas; 
 a fuel gas supply/exhaust portion configured to supply the fuel gas to the fuel cell and to exhaust the fuel gas from the fuel cell; 
 an oxidant gas supply/exhaust portion configured to supply the oxidant gas to the fuel cell and to exhaust the oxidant gas from the fuel cell; 
 a cooling portion configured to circulate a coolant through the fuel cell; and 
 a controller programmed to control the cooling portion to adjust a temperature of the coolant, wherein: 
 the controller is programmed to perform at least one of a transient increase control process and a transient decrease control process; 
 the controller is programmed to determine, in the transient increase control process, whether the temperature of the coolant is in a transient increase state in which a state of the temperature of the coolant is changed to a high-temperature state that deviates from a steady control state in which the temperature of the coolant is controlled to a steady temperature; 
 the controller is programmed to perform, when the controller determines that the temperature of the coolant is in the transient increase state, an oxidant gas pressure increase process; 
 the controller is programmed to control, in the oxidant gas pressure increase process, the oxidant gas supply/exhaust portion in a first period such that a target value of a pressure of the oxidant gas to be supplied to the fuel cell becomes higher than an operation target value corresponding to an operating state of the fuel cell system in the steady control state, the first period being a period during which the temperature of the coolant increases; 
 the controller is programmed to determine, in the transient decrease control process, whether the temperature of the coolant is in a transient decrease state in which the state of the temperature of the coolant is changed to the steady control state from the high-temperature state deviating from the steady control state; 
 the controller is programmed to perform, when the controller determines that the temperature of the coolant is in the transient decrease state, at least one of the oxidant gas pressure increase process and an output increase process in a second period, the second period being a period during which the state of the temperature of the coolant returns to a steady temperature state from the high-temperature state, the steady temperature state being a state of the temperature of the coolant in which the coolant is in the steady temperature; and 
 the controller is programmed to control, in the output increase process, the fuel cell to generate an output higher than a target output corresponding to a request output. 
 
     
     
       2. The fuel cell system according to  claim 1 , wherein
 the controller is programmed to perform both the transient increase control process and the transient decrease control process. 
 
     
     
       3. The fuel cell system according to  claim 1 , wherein
 the controller is programmed to perform both the oxidant gas pressure increase process and the output increase process in the transient decrease control process. 
 
     
     
       4. The fuel cell system according to  claim 1 , wherein
 the controller is programmed to determine the transient increase state of the temperature of the coolant based on either one of a first condition and a second condition; 
 the first condition is that the temperature of the coolant increases over an increase threshold temperature; 
 the second condition is that an output request to the fuel cell is an increase threshold output or more; 
 the controller is programmed to determine the transient decrease state of the temperature of the coolant based on either one of a third condition and a fourth condition; 
 the third condition is that the temperature of the coolant decreases over a decrease threshold temperature; and 
 the fourth condition is that the output request to the fuel cell is a decrease threshold output or less. 
 
     
     
       5. The fuel cell system according to  claim 1 , wherein:
 the first period is a period from a time point when the controller determines that the temperature of the coolant is in the transient increase state, until a time point when the temperature of the coolant increases to an increase end threshold temperature; and 
 the second period is a period from a time point when it is determined that the temperature of the coolant is in the transient decrease state, until a time point when the temperature of the coolant decreases to a decrease end threshold temperature. 
 
     
     
       6. A control method of a fuel cell system, the control method being for controlling supply of a fuel gas, an oxidant gas, and a coolant to a fuel cell to generate a power, the control method comprising:
 performing at least one of a transient increase control process and a transient decrease control process, wherein: 
 in the transient increase control process, it is determined whether a temperature of the coolant is in a transient increase state in which a state of the temperature of the coolant is changed to a high-temperature state deviating from a steady control state in which the temperature of the coolant is controlled to a steady temperature; 
 when it is determined that the temperature of the coolant is in the transient increase state, an oxidant gas pressure increase process is performed in a first period during which the temperature of the coolant increases, the oxidant gas pressure increase process being a process of setting a target value of a pressure of the oxidant gas to be supplied to the fuel cell to a value that is higher than an operation target value corresponding to an operating state of the fuel cell system in the steady control state; 
 in the transient decrease control process, it is determined whether the temperature of the coolant is in a transient decrease state in which the state of the temperature of coolant is changed to the steady control state from the high-temperature state deviating from the steady control state; 
 when it is determined that the temperature of the coolant is in the transient decrease state, at least one of the oxidant gas pressure increasing process and an output increase process is performed in a second period, the second period being a period during which the state of the temperature of the coolant returns to a steady temperature state from the high-temperature state, the steady temperature state being a state of the temperature of the coolant in which the coolant is in the steady temperature; and 
 in the output increase process, a target value of an output of the fuel cell is set to a value higher than a target value corresponding to a request output.